The present invention relates to analytical instruments for detecting and identifying trace levels of selected vapors, and i particular to portable instruments. The present invention has particular application to detection and identification of various vapors in gaseous media, such as air.
It is known to preconcentrate analytes in air samples by the use of sorbents, and thereby increase the sensitivity of detecting instruments. The aforementioned copending U.S. application Ser. No. 828,990 discloses the use of an absorption preconcentrating air sampler to increase the sensitivity of an analytical instrument. In such a sampler, a substantial portion of the analyte contained in a large volume of air becomes absorbed in a small volume of liquid extractant that can be injected directly into an analytical instrument, such as a liquid chromatograph. As compared with other methods, the direct absorption of an analyte from an arbitrarily large volume of air into a small volume of liquid extractant offers the advantages of low-temperature operation, simplicity, speed and flexibility. That device has proved effective for detecting hazardous analytes, such as highly carcinogenic primarily aromatic amines, when used with gas or liquid chromatographs.
It is also known to colorimetrically detect analytes by the use of Draeger tubes, in which selected reagents change color in predetermined ways in response to certain analytes. But the Draeger tubes are of relatively low sensitivity, utilizing a relatively large volume of reagent, and can effect measurements over a limited concentration range. Furthermore, this technique is of limited flexibility, since it is not easily adapted to frequent repetitive measurements.